Alloy coated steel article



Jan. 25, 1966 D. R. VlRZl ALLOY COATED STEEL ARTICLE Filed Dec. 18, 1963 INVENTOR. flfl/MLD PUBEETWPZ/ ATTOF/I/[y United States Patent Office 3,231,127 Patented Jan. 25, 1966 3,231,127 ALLOY COATED STEEL ARTICLE Donald Robert Virzi, Oak Park, Ill., assignor to American glan Company, New York, N.Y., a corporation of New ersey Filed Dec. 18, 1963, Ser. No. 331,599

. 8 Claims. (Cl. 220-52) This invention relates to a metal alloy coated steel member and more particularly to a steel member, coated with tin-zinc alloy, coupled to a tin-coated steel article.

A great many metal containers are made today that utilize a metal key to open the container by removing an integral metal trear strip. An example of such a container is shown in US. Patent No. 3,055,539.

The usual procedure is to attach the metal key to an end of the container by some suitable means such as soldering or welding. Thus the key is available and easily removable from the container when needed for opening. At present, keys for these key-open cans are generally made from zinc-coated steel wire. This zinc coating provides physical and anodic protection for the steel basis metal when exposed to a corrosive environment, such as is commonly found in the processing and storage of canned comestibles.

However, while providing the anodic protection for the steel basis metal a white corrosion product often forms on the surface of the zinc. This corrosion product is commonly called white rust and is probably a carbonate or oxide of zinc.

Since the zinc-coated key is generally coupled to a tin-coated steel container, the zinc not only offers anodic protection to the steel, which it covers, but also .to any exposed steel basis metal of the tinplate.

Because zinc is more electropositive than both iron and tin, it thus galvanically protects not only the iron, but also the tin. Zinc, which has an electrode potential of -|-0.7618, compared to the potential of +0136 for tin, is more active than tin and is therefore sacrificial to tin.

In addition to its anodic protection of the steel, some of the zinc generally alloys with the iron of the steel basis metal to form a' black colored deposit. This black deposit and the white corrosion product are quite unsightly and, hence, are very undesirable, since the consumer finds them objectionable.

It is therefore an object of the present invention to provide a coating for steel which will not develop an unsightly appearance when subjected to a" corrosive environment.

Another object of the invention is to provide a coated steel article whose coating will electrochemically protect the steel from corrosion.

Still another object of the invention is to provide a coating for steel which will not form white rust when exposed to a humid environment.

A further object of the invention is to provide a corrosion-resistant coating for steel keys that are conductively attached to a tin-coated steel container.

Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment thereof.

The above objects are accomplished by providing an article of manufacture having a tin-zinc alloy coated steel member, wherein tin is the major constituent of the tinzinc alloy. The alloy-coated member is coupled to a tin-coated steel article, whereby the alloy coating is electrochemically sacrificial to the steel and the tin coating, and the alloy coating prevents the formation of white corrosion products on the member and the red rusting of any exposed steel in the steel member when exposed to moisture.

Referring to the drawing:

FIGURE 1 is a top plan view showing a container with an opening key attached to the end thereof;

FIG. 2 is an enlarged sectional view taken substantially along the line 2--2 in FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken substantially along the line 33 in FIG. 1; and

FIG. 4 is an enlarged sectional view taken substantially along the line 4-4 in FIG. 1.

As a preferred or exemplary embodiment of the instant invention, FIG. 1 illustrates a container end 11 secured to the body of a container (not shown) by means of a conventional double seam 12. Conductively attached to the end 11, by means which will be explained more fully hereinafter, is a key 14. This key 14 is utilized in opening the container.

Both the end 11 and the key 14 (FIGS. 2 and 3) are made of steel basis metal coated with a suitable corrosionresistant metallic coating which will be described more fully hereinafter.

The end 11 is formed from conventional tinplate stock having a steel basis metal 16 coated with a layer of tin 18. This tin deposit is generally applied by means of electrodeposition, followed by a flow-brightening procedure well known to those skilled in the art. The coating of tin will generally have a thickness from 6X10 to 90 1O inch. Preferably the tin deposit will have a thickness from l5 10- to 60X 10- inch.

Although the electrodeposition and subsequent flowbrightening technique of applying the tin coating is preferred, such methods as vacuum deposition, gaseous deposition, or hot dipping may also be used.

The key 14 is formed from a piece of steel wire 19 and is bent to form a handle 20 and a shank 22. A major portion 24 of the shank 22 is flattened and provided with a slot 26 through which the tongue of the container-opening strip (not shown) is adapted to enter, when it is desired to open the container,

The wire 19, from which the key is made, is preferably a low-carbon steel. A tin-zinc binary alloy coating 30 is preferably applied to the wire 28 by suitable means, such as hot dipping, prior to forming the key 14. When hot dipping is used to apply the alloy coating30,- a

ternary alloy layer 32 of tin, zinc, and iron is formed between the outer coating 30 and the steel wire 19.

On the other hand, if the tin-zinc coating 30 is applied by means of electrodeposition, vacuum deposition, gaseous reduction, or mechanical plating, no intermediate alloy layer 32 is formed. The presence of the alloy layer 32 has not been found to be essential. A satisfactory electroplating technique is described on page 390 in the Metal Finishing Guidebook Directory, 1962 edition.

The composition of the alloy coating 30 will vary to some degree. However, in no case will less than 50% tin be present in the alloy. It has been found that the tinzinc alloy coating 30 will exhibit the most satisfactory resistance to corrosion when the tin is in the amount of to 96%, with the optimum corrosion-resistant properties obtained when the tin is from to 92%, with the balance being zinc. If less than 4% zinc is present, red rust may form on any exposed steel.

At the eutectic composition, 91% tin-9% zinc, the melting point of the alloy is 390 R, which is more than adequate to resist melting when the filled container, to which the key 14 is attached, is heated during a canning process.

As the tin content of the tin-zinc alloy increases, the resistance to white rusting also increases. However, the

resistance to red rusting decreases with increasing tin content. The hereinbefore mentioned composition range has been found to provide the best balance in providing adequate overall corrosion resistance.

It should be noted that the key 14 is generally formed from pre-coated wire stock. The slot 26 is punched after forming the key 14. Thus the inner surface 33 of the slot is not covered with the tin-zinc coating 30, but is, in fact, bare steel. This is also generally true of the ends 34, 36. It is thus apparent that the sacrificial anodic properties of the coating 30 are most important to prevent rusting of the exposed steel surface 33 and the ends 34, 36.

Although the thickness of the coating 30 may vary to a considerable degree, it should be no less than 1X10- inch and preferably no greater than 8.5 inch. It is to be understood that the maximum thickness is not critical, this maximum being controlled far more by economic factors than by corrosion factors. The preferred thickness is about 3.3 =10 inch.

The key 14 is preferably conductively attached to the end 11 by suitable means well known to those skilled in the art, such as welding or soldering. For the purposes of this invention and in the interests of manufacturing economy and speed, it is preferred that the key 14 be attached to the end 11 by spot resistance welding, thereby forming a conductive weld nugget 38 integral with both the key 14 and the end 11. The reason for the conductive attachment of the key 14 to the end 11 will be explained more fully hereinafter.

When the key 14 and the end 11, to which it is conductively attached, are placed in a corrosive environment,

such as a hot brine solution, used in the processing of canned meats, the tin-zinc coating will dissolve anodically in trying to electrochemically protect the container and bare steel present on the inner surface 33 of the slot 26 and the bare steel exposed on the ends 34, 36. Both the container and the bare steel react as a cathode.

Since the tin-zinc coating has a potential very close to the tin 18 of the end 11, the degree of dissolution of the coating 30 is very slight. However, there is suflicient electrochemical current flow present to prevent rust from forming on any exposed steel. In addition, no white corrosion products, such as are found in the case of zinc coatings, are formed on the tin-zinc coating 30.

Although it is preferred that the key 14 be conductively attached to the end 11 by means hereinbefore described, it may, in certain cases, be desirable to attach the key 14 by means of some nonconductive substance such as an organic adhesive. In such case the tin-zinc alloy 30 will not anodically protect the tin-coated steel of the end 11, since no electrical connection will lie therebetween.

In order to provide additional corrosion protection to the tin-zinc alloy 30 it may also be desirable to form a chromate coating on the surface of the alloy 30 by dipping the key 14 into a chromate or dichromate passivating solution, Well known to those skilled in the art.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be .made in the form, construction, and arrangement of the parts Without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. An article of manufacture, comprising: a tin-zinc alloy coated member, said tin-zinc alloy having tin as the major constituent; and a tin-coated steel article to which said alloy-coated member is coupled, whereby said alloy coating is electrochemically sacrificial to said tin coating and said alloy coating prevents the formation of corrosion products on said member and the red-rusting of any exposed iron in said member when exposed to a corrosive environment.

2. The article of claim 1 wherein said tin in said tinzinc alloy is in the amount of from to 96%.

3. The article of claim 2 wherein said tin is in the amount of to 92%.

4. The article of claim 1 wherein said tin-zinc alloy coated steel member is a wire opening key utilized for removing a tear strip in opening a container.

5. The article of claim 4 wherein said tin-coated steel article is an end of a tin-coated steel container.

6. The article of claim 5 wherein said tin-zinc coated steel member is welded to said tin-coated article.

7. The article of claim 5 wherein said tin-zinc coated steel member is soldered to said tin-coated article.

8. A one-piece wire opening key for metal cans, comprising: a handle and a shank; said key having thereon a coating of a tin-Zinc binary alloy wherein tin is in the amount of from 75 to 96%; said coating having a thickness of from 1 to 8.5 X 10- inch; and a slot in said shank through which a tongue of a container-opening strip is adapted to enter, the inner surface of said slot being bare steel.

References Cited by the Examiner UNITED STATES PATENTS 2,229,275 1/ 1941 Burns 220-52 2,258,610 10/1941 Hothersall 22052 THERON E, CONDON, Primary Examiner. 

8. A ONE-PIECE WIRE OPENING KEY FOR METAL CANS, COMPRISING: A HANDLE AND A SHANK; SAID KEY HAVING THEREON A COATING OF A TIN-ZINC BINARY ALLOY WHEREIN TIN IS IN THE AMOUNT OF FROM 75 TO 96%; SAID COATING HAVING A THICKNESS OF FROM 1 TO 8.5X10-4 INCH; AND A SLOT IN SAID SHANK THROUGH WHICH A TONGUE OF A CONTAINER-OPENING STRIP IS ADAPTED TO ENTER, THE INNER SURFACE OF SAID SLOT BEING BARE STEEL. 